Apparatus for heating by subatmospheric steam



' Sept. 26, 19335 c. A. DURHAM PrARA'rus r03 HEATING BY suanuosramficsum 4 Sheets-Sheet 3 Original Filed July 15. 19 27 Imfmfi [205/7512 AJulia 112 c. A. DUNHAM APPARATUS FOR- HEATING BY SUBATIOSPhERIC S TEAISept. 26, 1933.

Original Fi 1ed July 15, 1927 4 Sheets-Sheet 4 Im/enm [@7072 AzaniaPatented Sept. 26, 1933 PAT m OFFICE APPARATUS FOR HEATING BY QUE-ATMOSPHERIC STEAM Clayton A. Dunham, Glencoe, -lll., assignor to C. A.Dunham Company, Marshalltown, Iowa,

a corporation of Iowa Original application July 15, 1927, sci-m no.

205,978. Divided and this application February 25, 1929. Serial No.342,557

. 9 Claims.

This invention relates to an improved apparatus for heating bysub-atmospheric steam, and more particularly to improvements in amultiple-unit vacumn heating system. Such a system is particularlyadapted for use in very large buildings,

wherein different sections of the building are simultaneously subject todifferent temperature conditions, due to diiferent locations in thebuilding, diiferent distances from thesource of steam 10 supply,difierent exposures, diiferences' in building construction, or otherconditions, so that there are different heating requirements in thesedifferent building sections. This application is a division ofmycopend'ing application Serial No. 205,978, filed July 15, 1927. Inthis parent application, the new method of heating by sub-atmosphericsteam is claimed.

This system is an adaptation to the requirements noted hereinabove ofthe differential vacuum steam heating system disclosed and claimed in myPatent No. 1,644,114, granted October 4, 1927. Such a system includes asteam generator or other source of supply, from which steam is suppliedto the radiators at an'adjustable subatmospheric pressure. Athermostatically operated trap at the outlet of each radiator normallyprevents the escape of steam, but permits the escape of accumulatedliquid condensate and air to a. return main leading down to anaccumulator tank. Suitable'vacuum producing means serve to withdraw thisliquid condensate and air, vent the air, return the water to the steamgenerator, and maintain the necessary vacuum in the return main and alsothroughout the system. By means of a' suitable reducing valve in thesupply pipe, and suitable restricting orifices at the inlets of theradiators, the sub-atmospheric pressure of the steam delivered to theradiators may be varied, in accordance with the heat output de.- siredto meet the temperature requirements.- Dual control means is providedfor the vacuumproducing mechanism whereby it is automatically operatedto maintain a substantially constant dif-- ference in pressure betweenthe supply and return sides of the system, regardless of the absolutepressure maintained in the supply main, and is also operated inaccordance with the level or the accumulated liquid condensate in orderto return this water to the steam generator.

According tothe present invention, in its preferred embodiment, eachseparate section of the building is provided with a diiiermtial vacuumheating system of the type just briefly described. A single generator orgroup of boilers is provided for supplying steam to the several separatedistem might be advantageously used.

tributing systems, and the reducing valves for all oi. the systems aregrouped or centralized adjacent suitable temperature indicatinginstruments connected with certain key-rooms in each of the sections orthe building. These instru- 80 ments indicate the different simultaneoustemperature requirements in the different building sections, and inaccordance'with these indications the operator may suitably adjust thedifferent reducing valves so that the subatmospheric pressure of thesteam supplied to each unit or branch "of the system will correspond tothe heating requirement in that building section. The returns from theseveral distributing systems are lead back to a group of separatevacuum-producing 70 mechanisms, all of which discharge their accumulatedliquid condensates back to the common source of steam supply.

The principal object of this invention is to provide a new apparatus forheating large buildings, such as has'been briefly described'hereinaboveand as is disclosed more in detail in the description which follows.

Another object is to provide means whereby an auxiliarypressure-controlled unit may be temporarily substituted for any one ofthe similar units normally used in the several distributing systems.

Another object is to provide means whereby an auxiliary vacuum-producingmechanism may be substituted for the similar mechanism normally 35 usedin each of the systems.

Another object is to provide means whereby exhaust steam from an engineor other source may be distributed at the proper sub-atmosphericpressure to any one or all oi. the several distinct distributingsystems.

Other objects and advantages of this invention will be more apparentfrom the following detailed description ofone approved for .n ofapparatus suitable for carrying out the principles of this invention.

In the accompanying drawings:

Fig. 1 is a diagrammatic illustration of a large ofllce building whereinthis improved heating sys- Fig. 2 illustrates the essential parts of anyone distributing unit'of the heating system.

Fig. 3 is a plan view of the centralized supply and return portions ofthe heating system.

Fig. 4 is a vertical section through the boiler room and adjacentportions of the building, illustrating in elevation the mechanism shownin Fig. 3.

Fig. 5 is a detail elevation illustrating certain additions to andmodifications of the structure shown in Figs. 3 and 4, whereby exhauststeam of the building.

Fig. 6 is an elevation, partly in section, through one of the radiatorinlet valves and restricted inlet orifices.

Referring first to Fig. 1, which illustrates a large building of the newset-backconstruction, it will be noted that this building has beendivided graphically by dotted lines into eight separate blocks orsections A, B, C, D, E, F, G'and H. The section Dis not visible, but itslocation will be obvious from the drawings. It will be apparent that abuilding of this size is subject in different locations to a widelydiifering variety of temperature conditions. Certain portions of thebuilding will be continuously shaded or protected by adjoiningstructures, whereas other portions will be constantly exposed to the sunor air currents. These conditions will vary at different sides of thebuilding, and at different heights. As a general rule in this country,the heat requirements on the southern sides of buildings are not asgreat as on the northern exposures. The decreased cross-sectional areaand proportionately increased outside exposure of the upper portions ofthe building will usually increase the heat loss and require increasedradiation from the heating system. If the steam or other heating mediumwere supplied to all portions of the building at the same temperature,it will be apparent that ..this temperature would have to be sumcient tomeet the heat requirement of the coldest section of the building, andwould, therefore, be greatly in excess of the heat requirements in otherportions of the building. According to this invention, the building isdivided into a plurality of separate divisions or-sections, and theheating medium is supplied to the group of radiators in each section ata temperature suiiicient to meet the average heat requirement of. thatsection. The steam or other heating medium is supplied from a commonsource and the temperature of the steam delivered to each section of thebuilding is controlled by the sub-atmospheric pressure of the steamsupplied to this section. More specifically, the pressure of the steamtaken from the common source is reduced when it is delivered to eachseparate distributing system so that the sub-atmospheric pressure of thesteam supplied to that system will correspond to the steam temperaturenecessary to meet the average heating requirements in that section. Inthe example illustrated, the main lower section of the building has beendivided into four corner blocks or divisions A, B, C and D. The nextlargest setback has been divided into two sections E and F.Presumptively one oi these would be a northern exposure and the other asouthern exposure. The

two upper set-backs have been divided vertically into two sections G andH. The example shown is merely illustrative, and each building would bedivided into more or less'sections, of varying size and location,according to the particular conditions presented by the location andconstruction Referring now to Fig; 2, I will briefly describe a singleunit oi a differential vacuum steam heating system, such as is disclosedand claimed in my'Patent No. 1,644,114, hereinabove referred to. Steamfrom any suitable generator is supplied through the reducing valve Kandsupply main L to the radiators M. Condensate and air are drawn out ofthe radiators through thermostatic traps N and through return main .0 tothe accumulator tank P. The vacuum producing mechanism incumulatedliquid condensate in the tank P.

Steam passes from the boiler or other source of supply through pipe 1and cut-off or gate valves 2, to andthrough the reducing valve K intothe supply main L. The reducing valve K may be of the well known formembodying balanced cutoff valves whose movements to closed or openpositions are governed by the enclosed pressure diaphragm 3 and thebalanced weights 4 and 5. The diaphragm 3 is subject on one side to thesteam pressure in supply main L, by means of the pipe 6 connected at oneend to the housing of the diaphragm and at the other end to the supplymain at a point sufflciently remote from the valve K to be uninfiuencedby pressure disturbances in the vicinity of the valve. This reducingvalve Kdiifers from similar valves heretofore in use, in the fact thatthe balancing weights 4 and 5 are so proportioned and positioned that adesired sub-atmospheric pressure may be maintained in the supply main L,while a higher pressure (either sub-atmospheric or super-atmospheric)exists in the supply pipe 1. By properly adjusting the weights 4 and 5(or other equivalent spring or balancing devices which may be used), anydesired degree of vacuum may be maintained in the supply pipe L.Preferably a pressure gauge 7- is provided to indicate this ,vacuum orsubatmospheric pressure.

Instead of the manually adjusted reducing valve K, as shown in Fig. 2,an automatic temperature controlled valve might be substituted, asdisclosed for example in my Patent No. 1,644,114, hereinabove referredto.

The risers 8 lead from the supply main L to furnish steam to the severalradiators M, two of which are here shown by way of example, although itis to be understood that any desired number of radiators may be used. Ina similar 1- manner the risers 9, here shown, lead to. radiators on afloor above those indicated in the drawings. Steam passes from the riser8 through inlet valve 10 into the radiator This inlet valve willnormally be open when the radiator is in service to permit free passageof steam from the supply main to the radiator, but the valve may beclosed when any individual radiator is not to be used for heatingpurposes.

As indicated in Fig. 6, an orifice plate is interposed in the pipeleading from the valve 10 to the radiator, this plate restricting theflow of steam so that for average pressures in the supply piping, themaximum quantity of steam that the radiator will receive is fixed andproportioned to the condensing capacity of the radiator. The

orifices 111 in the plates 110 of the various radiradiator M is athermostatically operated steam trap N, which normally retains the steamwithin the radiator, but permits the outflow of accumulated liquidcondensate and air through pipe 11 to the return main 0. Thisthermostatic steam trap is preferably of the type emb dyin a valve whichis moved toward or from its seat by the expansion or contraction of afluid-filled thermostatic disc.

The liquid condensate and air flow downward by gravity, assisted by thesuction of the vacuum producing mechanism R, hereinafter described,through the return main 0 and suction strainer 12 into the accumulatortank 1?. The water of condensation and air accumulating in the supplymain L is vented through the pipe 13 and float and thermostatic trap 14,and pipe 15 to the return main 0, and is afterwards handled along withthe condensates from the radiators. I

The suction producing mechanism R, as here shown, comprises a tank 16partially filled with water, from the lower portion of which a pump 1'7withdraws water through pipe 18 and forces this water upwardly through aJet exhauster 19 back through pipe 20 into the upper portion of tank 16.This hurling water circuit produces a suction in the casing of ejector,19, which draws up the water and air from the lower portion of theaccumulator tank P, through pipe 21, these gases and condensates beingcarried along with .the water of the hurling circuit and discharged intothe tank 16. A one-way check valve 22 in pipe 21 prevents the return ofthese materials to the accumulator tank. The gases discharged into tank16 are vented to the atmosphere through pipe 23, provided with checkvalve 24. The pipe 23 is here shown as discharging into a sewerconnection at 25. A second outlet from the centrifugal pump 17 leadsthrough valve 26, pipe 2'7, check valve 29 and cut-ofl valve 28 back tothe steam generator, or to a feed water heater, stain the installationhereinafter described. A float 30 in the tank 16 operates, when thelevel of accumulated liquid in the tank 16 has reached a certain height,through the link and lever connections 31 to open the valve 26 andpermits the pump 1'1 to force water out through pipe 27 and check valve29.

The motor 32 which drives the pump 17 is connected by. wires 33 with thestarter 34, which is under the separate and independent, control of twodistinct switch mechanisms as and as. Switch 35 is controlled throughlever mechanism 37 by a float'38 positioned in the accumulator tank P.When a certain amount of liquid condensate has gravitated through returnmain 0 into this tank, the float 38 will be lifted sumciently to closethe switch 35, which results in starting the motor 32 and the vacuumproducing mechanism commences to function to withdraw the condensatesand air in tank P and discharge them into tank 16. Here the gases arevented through pipe 23, and when suilicient water has accumulated, it isreturned to the boiler or to the feed water heaterv in the manneralready described. v

Switch 36 is controlled by the diflerential pressure regulator S, whichcomprises a movable diaphragm adapted in a well known manner to open orclose the switch 36 through the lever connections 39. The diaphragm ofdifferential pressure regulator S is subject on its opposite sides tothe pressure existing in the supply and return mains, one side beingconnected through pipe 40 with the supply main L, and the other sidethrough pipedl withthereturnmalno. Sincebothpipes 40 and 41' will becomefilled with liquid condensate, they are initially 'fllled with water andthe vertical lengths of the two pipes must be of the same verticalheight, as shown, in order to equalize the water head pressing on eachside of the diaphragm of the pressure regulator. when the diflerence inpressure between the two mains falls below a certain minimum, switch 36will be closed, whereupon the motor 32 will be started and the pumpingmechanism will operate to suck liquids and air from the tank P andthence from the return main 0. This will lower the pressure in thereturn main 0 and the pump-will continue to operate until a desiredmaximum pressure differential is established between the return andsupply mains, whereupon switch 36 will be opened to stop the motor 32.

In the normal operation of the system, as so far described, the reducingvalve K is adjusted so as to maintain the desired degree of vacuum inthe supply main L. Asis well known, steam will be generated atatmospheric pressure at 212 F. Under higher pressures steam will begenerated at higher temperatures, and conversely under a vacuum, steamwill be generated at lower temperatures, the temperature of the steamdepending upon the degree .of vacuum existing in the system. Thisprinciple is utilized in this heating system sothat by varying thesub-atmospheric pressure in the supply main L, the temperature of thesteam delivered to the radiators M is correspondingly varied so thatsteam at comparatively low temperatures may be maintained in theradiators when prevailing weather conditions necessitate only a mildradiation of heat from the radiators. Steam may be more economicallygenerated at lower temperatures, and it is more emcient and economicalto maintain a constant supply of steam at a comparatively lowtemperature than an intermittent supply of steam at a highertemperature.

, While the degree .of vacuum existing in the system may be varied fromatmospheric pressure, or slightly above, to as low as perhaps 24 inchesof vacuum, in order to obtain the desired heating effect from theradiators, it is also desirable that a substantially constant andrelatively small difference in pressure be maintained between the supplyand return sides of the radiators, this pressure differential being justsumcient to insure the proper circulation of steam and provide forwithdrawing the condensates and air. Accordingly, the vacuum producingsystem is adjusted to operate to maintain this fixed pressuredifferential between the supply and return mains, but as hereinafterexplained, in order to maintain this fixed differential, it will alsofunction to maintain the desired degree of vacuum throughout the system.

When starting the operation of this system,

with steam in the pipe 1, the pumping mecha-.

nism R is put into operation to create a suction in the system. At thistime the system will be empty of steam and the thermostatic traps N willbe open. There will be no substantial difference in pressure between thereturn and sup-- traps until-such time as suiiicient condensate has 150accumulated to open these valves and-permit its withdrawal. The pumpingmechanism R. will continue to operate until the sub-atmospheric pressurein return main 0 (which is now out of: from the supply main L bytheclosed traps N) has been lowered until the necessary pressuredifierential has been attained, whereupon the control mechanism S willoperate the switch 36 to stop the motor 32. As steam condenses in theradiators M, the pressure in the radiators and supply main L will belowered below the subatmospheric pressure for which the valve K is set,and this valve will open and admit more steam to the supply main andradiators, thus keeping the radiators full of steam at the desiredsub-atmospheric pressure. The thermostatic traps N will automaticallyopen to permit the accumulated condensate and air to pass out into thereturn main 0, and will again be closed when steam attempts to passthrough these traps. This entry of air and condensate into thereturn-main 0 will somewhat raise the pressure in this main so that thediiference in pressure between the return main and supply main may fallbelow the necessary minimum, whereupon the control device S will operatethe switch 36 to start the motor 32, and the pumping mechanism R willbegin functioning at once to again reduce the pressure in the returnmain 0. The pumping mechanism' R will only operate at such intervals'asis necessary to maintain the pressure difierential between the supplyand return mains, or when the accumulation of liquid in the accumulatortank P necessitates its removal to tank 16 and thence to the generator.

The object sought to be attained by this systemis the substantiallyconstant emission of heat from the radiators at a rate just suflicientto replace the heat lost from the building. This is accomplished, not byturning the radiators on or off at intervals, but by changing thetemperature of the steam maintained in the radiators, and this in turnis accomplished by varying the sub-atmospheric pressure of this steam.This pressure variation is accomplished, in the system here disclosed,by adjustment of the reducing valve K.

Having thus briefly explained the operation of one unit of the improveddifferential vacuum heating system, I will now return to the explanationof the multiple-unit system which forms the particular subject matter ofthe present invention. In general, it may be stated that a system suchas has just been briefly described is utilized to independently heateach of the sections A to H inclusive of the building, as shown in Fig.

1. Referring now to Figs. 3 and 4, at W is shown thesteam generatingplant, consisting in this case of a group of boilers 42 to 47 inclusive.At X is shown the grouped or centralized control valves for the severalbranches of the system, and at Y is similarly grouped the pumpingmechanism for the several units. At Z is indicated the e neers room orcontrol room, wherein the operator may observe the temperatureconditions in the various portions of the building.

The several boilers 42 to 47 inclusive each feeds through a pipe 48 andvalve 49 into the high pressure header 50. Steam is fed from highpressure header 50 through reducing valves 51 and pipes 52 to the lowerpressure headers 53 and 54. Steam is supplied through the several pipes1 leading from headers 53 and 54 to the group of reducing valves K to Kinclusive to the supply pipes L to U inclusive of the eight distinctbranch heating systems which supply heat to the respective sections A toH or the building, as indicated in Fig. 1. At an adjacent location, thereturn pipes O to 0' of these respective branch heating systems leadback to the accumulator tanks P. to P', respectively. The condensatedelivery pipes 27. of the several branch systems all feed into a commonheader pipe 55, leading through check valve 56 to the 'feed water heaterindicated diagrammatically at 57. A pair of similar boiler teed pumps 58and 59 connected in multiple so that either one or both may be used,serve to pump water from the feed water heater 5'7 through pipe 60 andheader 61 back into the several boilers 42 to 47 inclusive. By means ofthe several valves 62 and feed pipes 63, the water may be fedselectively from header 61 into anydesired boiler or boilers.

Steam may flow from the low pressure header 53 through pipe 64 and theauxiliary reducing valve K (similar in all respects to any one of thereducing valves K to K), into the by-pass pipe 65 positionedtransversely of the several supply pipes L1 to L8 inclusive. From thebypass pipe 65, branch pipes 66 lead through outofi valves 67 into therespective supply pipes L to L This reducing valve K and by-pass 65serve as an emergency control valve which may be substituted for any oneof the main reducing valves K to K", respectively. In a similar manner,branch return pipes 68 lead through cut-off valves 69 into the by-passpipe 70 which feeds into an auxiliary accumulator tank P The auxiliarypumping unit R feeds back into the header 55 similarly to the mainpumping units R to R inclusive. By suitably manipulating the cut-oilvalves 28 and 69, the auxiliary pumping unit may be substituted for anyone of the units R to R". In this way, anyone of the pumping units maybe withdrawn from service when repairs are necessary, withoutincapacitating the corresponding branch heating system.

In a certain key-room '11 (see Fig. 1) in each of the sections A to Hinclusive, which rooms are selected to give the average temperatureconditions in each respective section, are located thermometers orthermostats which respectively actuate certain indicating instruments'72 in the instrument room Z. By means of these indicators 72} theengineer or operator can see at any time the temperature conditionsexisting in each of the several sections of the building and canregulate the reducing valves K accordingly to bring the temperatures toany desired normal. For example, let us suppose that it is desired tomaintain a temperature of 70 F. throughout the building, but theengineer notes that the indicator 72 corresponding to the section Gindicates that a'temperature lower than this, for example, 65", prevailsin that section or the building. Assuming that the reducing valve Kcontrols the branch heating system leading to section G, the

engineer will adjust this valve so as to increase the pressure (ordecrease the vacuum) of the steam supplied to this branch heatingsystem. This will increase the temperature of the steam delivered tothis respective section of the building ,and will bring the temperatureback to normal. On the other hand, let us suppose that one of theindicators shows that the temperature in building section F has becometoo high, for example F. Assuming that the reducing valve K controlsthis branch heating system, the engineer will adjust this valve so as todecrease the pressure (that is increase the vacuum) in the supplypipe 1. leading to this section oi the building. This will decrease thetemperature oi the steam deliveredto this branch heating system, and theresulting decreased radiation irom the radiators in this section oi thebuilding will bring the temperature back to normal. Ii desired, pressureindicators 73 may also be located in the instrument room Z showing therespective sub-atmospheric pressures existing in the several branchheating systems. Other pressure indicators will also be located eitherin the instrument room or adjacent the several pumping units to showthat the proper pressure diiierential is being maintained betweenthesupply and return pipes of each branch system.

The distinct advantage-oi this system resides in the iact that steam oivarious temperatures can be simultaneously furnished to diflerent partsoi the same building having diiierent exposures and different heatlosses. The amount of heat waste is minimized throughthe prevention oioverheating an unexposed section in order to keep the exposed sectioniully heated. With this system it is possible to maintain the entirebuilding at a substantially uniiorm temperature without continuallyturning on and of! the radiators in those portions oi the building whereless heat is required. The centralized system oi control permits theentire system to be regulated by a single operator who is alwayscognizant oi the temperature conditions prevailing in any. part oi thebuilding.

While in theexample here illustrated, we have shown a steamgeneratorcapable oi developing high pressure steam, this steam pressurebeing brought down by reducing valves beiore it is delivered to thelow-pressure headers 53 and 54, it is not at all essential tothe-operation oi this system that high pressure steam be developed.

The pressure in the boiler need notexceed the pressure required to heatthe most exposed portion oi the building, and this boiler pressure maycities to have central steam supplied from an outside sourcefinstead oiby a boiler plant in the building. In such an installation the steamwould be delivered to the low pressure headers 53 and 54 throughsuitable reducing valves in a similar manner to that already described.In such a system, that'portlon oi the apparatus which is utilized todeliver the condensate-back to the boiler could be eliminated.

In Fig. 5 is illustrated a modification whereby exhaust steam iromengines-or other high pressure apparatus may be utilized. A header '74positioned parallel with the low pressure header.

54 is connected through branch pipes '15 in which are located reducingvalves '76 and cut-oi! valves 77, with the several supply mains L. Theexhaust steam header '74 may. take the] place oi the by-pass pipe 65,already described, or may be arranged in parallel therewith. Thereducing valves'lcmaybesimilarinallrespectstotl ie the reducing valve ineach oi' these pipes, each reducing valves K, already described, and bysuitably adjusting these valves and the cut-oi! valve 7'7, the exhauststeam may be fed into any or all of the supply pipes L, either simultwith or as a substitute for the steam supplied direct from the boilersthrough the reducing valves K. It will be noted that this exhaust steamis "delivered directly into the vacuum mains L, thus making possible areducing oi the pressure in the exhaust pipes and adding materially tothe power. oi the engines. v

I claim:

1. :In a steam heating system, a header receiving steam irom a source ofsupply, a plurality oi distributing systems each system including asupply pipe and a reducing valve through which the supply pipecommunicates with the header, an auxiliary reducing valve communicatingwith the header, and a by-pass pipe leading irom the auxiliary valve andhaving valved branches leading respectively to the supply pipes oi alloi the systems.

2. Ina steam heating system, a header receiving steam irom a source oisupply, a plurality of distributing systems each system including asupply pipe and a reducing valve through which the supply pipecommunicates with the header, a second source of steam supply, andindependent connections irom this source to each oi the supply pipes atthe low pressure side oi of these independent connections including areducing valve.

3. In a steam distributing system, a source oi steam, a plurality oidistinct distributing systems each receiving steam at sub-atmosphericpressure from the source,each system comprising a means for regulatingthe sub-atmospheric pressure oi the steam supplied to the system inaccordance with the heat output desired in that system, said regulatingmeans comprising a vacuum-producing means ior maintaining thesub-atmospheric pressure in that system, and

a control means ior maintaining a pressure diiierential between theinlet and outlet sides oi the system suflicient to insure a flow oisteam through the system, an auxiliary vacuum pro-' ducing means, and aby-pass pipe having branches connecting thelast named means with" theoutlet side oi each oi the systems.

4. In steam heating apparatus, a source oi steam, a plurality ofdistinct distributing systems each receiving steam irom the source, eachsystem comprising a group of radiators, a supply pipe leading from thesource and having 188a branches leading to each radiator, exhaustingmeans ior withdrawing air and condensate irom the radiators withoutpermitting the escape oi steam therefrom, and separate restricting meanspositioned in each supply pipe and in each branch thereoi for separatelycontrolling the quantities oi steam delivered to each distributingsystem and to each radiator therein, the exhausting means and therestricting means in the supply pipes cooperating to separately maintainthe steam in each separate group oi radiators at a distinctsub-atmospheric pressure which is determined by the setting oi therespective restricting means in each supply pipe.

5. In a steam heating apparatus, a steam generator, a plurality oidistinct distributing systems each receiving steam irom the generator,each system comprising radiating means, means ior separately regulatingthe sub-atmospheric pressure oi the steam supplied to the system inaccordance with the heat output desired in the space heated by thatsystem, and means for withdrawing non-condensable gases and condensatefrom the system and venting the gases, and means for collecting andreturning the condensate from the several systems to the generator.

6. In a steam heating apparatus, a steam genorator, a header suppliedwith relatively high pressure steam from the generator, a plurality ofseparate distributing systems each supplying steam at sub-atmosphericpressures to different portions of a building, each system comprising asupply pipe, radiating means, 'a reducing valve in the supply pipe forcontrolling and adjusting the sub-atmospheric pressure of the steamsupplied from the header to the radiating means, a return pipe throughwhich non-condensable gases and condensate are withdrawn from theradiating. means, means for maintaining a substantially constantdiflerence in pressure between the supply and return pipes, andmeans forventing the non-condensable gases, and means for collecting thecondensate from the several systems and returning it to the generator.

'1. In a steam heating apparatus, a source oi steam, a plurality ofdistinct distributing systems each system comprising radiators, a supplyconduit leading from the source and having branches leading to theseveral radiators, an exhausting means, a return conduit having branchesleading from the radiators, the return conduit connecting with theexhausting means, traps at the outlets of the radiators, a reducingvalve in the supply conduit, the exhausting means functioning tomaintain a pressure differential between the supply and return conduitssufllcient to insure a :ilow of steam into the radiators and cooperatingwith the reducing valveto maintain the steam in the radiators at asub-atmospheric pressure which is determined by the setting of the valveand which may be varied in accordance with the heat output desired inthat particular distributing system, the reducing valves being locatedin a centralized group to permit of coordinated control of the severaldistributing systems.

8. In a steam heating apparatus, a source of steam, a plurality ofdistinct distributing systems each system comprising radiators, a supplyconduit leading from the source and having branches leading to theseveral radiators, an exhausting means, a return conduit having branchesleading from the radiators, the return conduit connecting with theexhausting means, traps at the outlets of the radiators, a reducingvalve in the supply conduit, the exhausting means functioning tomaintain a pressure differential between the supply and return conduitssufiicient to insure a flow oi. steam into the radiators and cooperatingwith the reducing valve to maintain the steam in the radiators at asubatmospheric pressure which is determined by the setting of the valveand which may be varied in accordance with the heat output desired inthat particular distributing system, the reducing valves and theexhausting means being respectively arranged in centralized groups topermit of coordinated control oi the several distributing systems.

9. In a steam heating apparatus, a source of steam, a plurality ofdistinct distributing systems each system comprising radiators, a supplyconduit leading from the source and having branches leading to theseveral radiators, an exhausting means, a return conduit having brancheslead-' ing from the radiators, thereturn conduit connecting with theexhausting means, traps at the outlets of the radiators, a reducingvalve in the supply conduit, the exhausting means functioning tomaintain a pressure differential between the supply and return conduitssuflicient to insure a flow of steam into the radiators and cooperatingwith the reducing valve to maintain the steam in the radiators at asub-atmospheric pressure which is determined by the setting of the valveand which may be varied in accordance' with the heat output desired inthat particular distributing system, the reducing valves being locatedin a centralized group, and a centralized group of means positionedadjacent the grouped valves for indicating the temperature CLAYTON A.DUNHAM.

